Array Deletion at Middle Index in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after deleting the middle element?

Given the array [10, 20, 30, 40, 50], the middle element is removed. What is the resulting array?

DSA Typescript

const arr = [10, 20, 30, 40, 50];
const mid = Math.floor(arr.length / 2);
arr.splice(mid, 1);
console.log(arr);

A [10, 20, 30, 40]

B [20, 30, 40, 50]

C [10, 30, 40, 50]

D [10, 20, 40, 50]

💡 Hint

Remember that array indices start at 0, and splice removes elements starting at the given index.

The middle index for an array of length 5 is 2 (0-based). Removing the element at index 2 (which is 30) results in [10, 20, 40, 50].

❓ Predict Output

intermediate

Output after deleting middle element from even-length array

What is the output after deleting the middle element from [5, 15, 25, 35, 45, 55] using the code below?

DSA Typescript

const arr = [5, 15, 25, 35, 45, 55];
const mid = Math.floor(arr.length / 2);
arr.splice(mid, 1);
console.log(arr);

A [5, 15, 25, 45, 55]

B [15, 25, 35, 45, 55]

C [5, 15, 25, 35, 45]

D [5, 15, 35, 45, 55]

💡 Hint

For even length arrays, Math.floor(length/2) gives the higher middle index.

Array length is 6, so mid = 3. Removing element at index 3 (which is 35) results in [5, 15, 25, 45, 55].

🔧 Debug

advanced

Potential issue when not using Math.floor for middle index

Consider this code snippet that tries to delete the middle element from an array. What is the potential issue with using arr.length / 2 directly?

DSA Typescript

const arr = [1, 2, 3, 4, 5];
const mid = arr.length / 2;
arr.splice(mid, 1);
console.log(arr);

A mid becomes a float number; indices should be integers explicitly.

B splice cannot remove elements from arrays.

C arr.length is undefined.

D console.log is called before splice.

💡 Hint

Check the type of mid; best practices recommend explicit integer conversion.

arr.length / 2 results in 2.5 (float). Although JS truncates it to 2 correctly here, using Math.floor(arr.length / 2) ensures an explicit integer index for clarity and reliability.

🧠 Conceptual

advanced

What is the time complexity of deleting the middle element from an array?

If you delete the middle element from an array of size n, what is the time complexity of this operation?

A O(log n) because of binary search to find middle.

B O(1) because splice removes element instantly.

C O(n) because elements after the middle must be shifted left.

D O(n^2) because all elements are copied twice.

💡 Hint

Think about what happens to elements after the removed one.

Deleting an element in the middle requires shifting all elements after it one position left, which takes O(n) time.

🚀 Application

expert

After multiple middle deletions, what is the final array?

Starting with [2, 4, 6, 8, 10, 12, 14], you delete the middle element 3 times in a row using the same method: find middle index as Math.floor(length/2) and remove that element. What is the final array?

DSA Typescript

let arr = [2, 4, 6, 8, 10, 12, 14];
for (let i = 0; i < 3; i++) {
  const mid = Math.floor(arr.length / 2);
  arr.splice(mid, 1);
}
console.log(arr);

A [2, 4, 6, 10, 12]

B [2, 4, 12, 14]

C [2, 4, 6, 12, 14]

D [2, 6, 10, 12]

💡 Hint

Perform each deletion step by step, updating the array each time.

Step 1: length 7, mid=3, remove 8 → [2,4,6,10,12,14] Step 2: length 6, mid=3, remove 10 → [2,4,6,12,14] Step 3: length 5, mid=2, remove 6 → [2,4,12,14]

Practice

1. What does deleting the middle element from an array mean?
Example: [1, 2, 3, 4, 5] Delete the middle element.

easy

A. Remove the element at index 2 (value 3) from the array

B. Remove the first element (value 1) from the array

C. Remove the last element (value 5) from the array

D. Remove all elements except the middle one

Solution

1. Step 1: Identify the middle index of the array

   The array has 5 elements, so middle index = floor(5/2) = 2.

2. Step 2: Remove the element at the middle index

   Removing element at index 2 removes the value 3 from the array.

3. Final Answer:

   Remove the element at index 2 (value 3) from the array -> Option A

4. Quick Check:

   Middle index = 2, remove element 3 [OK]

Hint: Middle index = floor(length/2), remove that element [OK]

Common Mistakes:

• Removing first or last element instead of middle
• Using length/2 without floor for odd length
• Confusing index with value

2. Which TypeScript code correctly deletes the middle element from array arr?

easy

A. arr.removeAt(Math.floor(arr.length / 2));

B. arr.splice(Math.floor(arr.length / 2), 1);

C. arr.delete(Math.floor(arr.length / 2));

D. arr.pop(Math.floor(arr.length / 2));

Solution

1. Step 1: Identify correct method to remove element by index in TypeScript

   TypeScript arrays use splice(index, count) to remove elements at a specific index.

2. Step 2: Use Math.floor(arr.length / 2) to get middle index

   This expression correctly calculates the middle index for deletion.

3. Final Answer:

   arr.splice(Math.floor(arr.length / 2), 1); -> Option B

4. Quick Check:

   splice + floor middle index = correct deletion [OK]

Hint: Use splice with floor(length/2) to delete middle [OK]

Common Mistakes:

• Using non-existent methods like delete or removeAt
• Using pop() which removes last element only
• Not flooring the middle index calculation

3. What is the output of this TypeScript code?

let arr = [10, 20, 30, 40, 50];
arr.splice(Math.floor(arr.length / 2), 1);
console.log(arr);

medium

A. [20, 30, 40, 50]

B. [10, 20, 30, 40, 50]

C. [10, 20, 30, 50]

D. [10, 20, 40, 50]

Solution

1. Step 1: Calculate middle index

   Array length is 5, so middle index = floor(5/2) = 2.

2. Step 2: Remove element at index 2

   Element at index 2 is 30, so removing it results in [10, 20, 40, 50].

3. Final Answer:

   [10, 20, 40, 50] -> Option D

4. Quick Check:

   Removed element 30 at index 2 [OK]

Hint: Remove element at floor(length/2) index [OK]

Common Mistakes:

• Not flooring index, causing wrong removal
• Removing wrong element index
• Expecting original array unchanged

4. Find the error in this code that tries to delete the middle element:

let arr = [5, 10, 15, 20];
arr.splice(arr.length / 2, 1);
console.log(arr);

medium

A. console.log syntax is incorrect

B. splice method does not exist on arrays

C. Using arr.length / 2 without floor causes wrong index

D. splice removes all elements, not one

Solution

1. Step 1: Check middle index calculation

   arr.length / 2 = 4 / 2 = 2 (number), but for even length arrays, middle index should be floor(4/2) = 2, so this seems correct but in TypeScript splice expects integer index.

2. Step 2: Verify if index is integer

   arr.length / 2 is 2 (integer), so no error here. But if length was odd, it would be float. The main issue is that for even length arrays, middle is ambiguous; usually floor is used to pick index 2.

3. Step 3: Identify actual problem

   In this code, no floor is used but division results in integer 2, so no error. However, if length was odd, index would be float causing error. So best practice is to use Math.floor to ensure integer index.

4. Final Answer:

   Using arr.length / 2 without floor causes wrong index -> Option C

5. Quick Check:

   Always floor middle index for splice [OK]

Hint: Always floor middle index before splice [OK]

Common Mistakes:

• Not flooring index causing float error
• Thinking splice removes all elements
• Misunderstanding console.log usage

5. Given an array arr of even length, how can you delete the lower middle element?
Example: arr = [2, 4, 6, 8] After deletion, output should be [2, 6, 8].

hard

A. arr.splice(Math.floor(arr.length / 2) - 1, 1);

B. arr.splice(Math.ceil(arr.length / 2), 1);

C. arr.splice(arr.length / 2, 1);

D. arr.splice(arr.length / 2 + 1, 1);

Solution

1. Step 1: Understand middle elements in even length array

   For even length 4, middle indices are 1 and 2 (0-based). Lower middle is index 1.

2. Step 2: Calculate index to delete

   Math.floor(4/2) = 2, subtract 1 to get lower middle index = 1.

3. Step 3: Use splice to delete element at index 1

   arr.splice(1, 1) removes element 4, resulting in [2, 6, 8].

4. Final Answer:

   arr.splice(Math.floor(arr.length / 2) - 1, 1); -> Option A

5. Quick Check:

   Lower middle index = floor(length/2)-1 [OK]

Hint: Lower middle = floor(length/2) - 1 for even arrays [OK]

Common Mistakes:

• Deleting upper middle instead of lower middle
• Not adjusting index for zero-based arrays
• Using ceil instead of floor